DIAGNOSIS
Escherichia coli and E. albertii grow on routine diagnostic media. Differentiation of E. coli isolates is important to distinguish pathogenic from non-pathogenic types. Pathogenic E.
coli are quite often haemolytic, and most of the animal strains are strongly lactose-fermentings. A presumptive identification is made from growth characteristics and/or biochemical tests. Serotyping is a well - established and a valuable method based on differences in cell wall polysaccharides (O antigens), capsular polysaccharides (K antigens), flagellar proteins (H antigens) and fimbriae (F antigens). Presently there are more than 170 O antigens, 80 K antigens and 56 H antigens known. In ETEC of animal origin, F-antigen determination is of importance. Particular media (e.g. E medium, minca agar) are required for sufficient expression of fimbriae. Commercial test kits such as latex agglutination tests or specific antisera are available for the detection of F antigens. An enzyme-linked immunosorbent assay (ELISA) measuring E. coli K99 antigen is also available commercially. Demonstration of enterotoxins can be performed by ELISA and enzyme immunoassay (EIA)(20). Polymerase chain reaction (PCR) and other procedures, including pulsed- field gel electrophoresis (PFGE), random amplified polymorphic DNA(RAPD) analysis, amplified fragment length polymorphism (AFLP) and ribotyping, are also often used to determine virulence factors in Escherichia spp. and to further characterize isolates within a distinct serotype(2).
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